With the development of digital technology in electronic devices, recent years have seen a rise in the demand for storage elements which have larger capacity and are nonvolatile, for storing data such as music, images, and information. As one measure to respond to such demand, attention has been placed on storage elements which use a material whose resistance value varies according to the electrical pulse applied, and continues to hold such state.
FIG. 9 is a cross-sectional view of a main section which shows the structure of a conventional example of such a nonvolatile storage element (for example, see PTL 1). As shown in FIG. 9, this nonvolatile storage element is a memory element (nonvolatile storage element) including one resistor 932 and one switching structure (transistor). In this nonvolatile storage element, a source region 921a and a drain region 921b are formed on a semiconductor substrate 920, a gate insulating layer 922 and a gate electrode 923 are formed on the semiconductor substrate 920 which contacts with the source region 921a and the drain region 921b, a contact plug 925 is formed in an inter-layer insulating film 924 with the contact plug 925 being electrically connected to a lower electrode 931, and the resistor 932 and an upper electrode 933 are sequentially formed on the lower electrode 931.
As substances making up the resistor 932, nickel oxide (NiO), titanium oxide (TiO2), hafnium oxide (HfO), niobium oxide (NbO2), zinc oxide (ZnO), zirconium oxide (ZrO2), tungsten oxide (WO3), cobalt oxide (CoO), GST (Ge2Sb2Te5), and PCMO (PrxCa1-xMnO3), and so on, are used. Such transition metal oxides are known to show a particular resistance value when a particular voltage is applied or by the application of a particular voltage through a particular application method, and continue to hold such resistance value until a new voltage or current is applied.